The prior art is replete with “lean-to-turn” mechanisms that enhance the turnability of wheeled devices having parallel pairs of wheels. Such mechanisms are usually in the form of trucks and axles designed to cause two parallel wheels to turn in unison when the wheeled device is tilted to one side or the other. One of the most common and well-known instances of this is in skateboards and “quad” skates such as the wheeled skate disclosed in U.S. Pat. No. 3,442,523. The '523 patent discloses a conventional roller skate having two pairs of wheels. Each pair of wheels has a wheel mount assembly including an angled shaft and an axle that is common to the paired wheels. Leaning the skate to one side causes the skate “shoe” portion to rotate about the wheel assembly shafts which in turn causes each common axle and the paired wheels attached thereto to rotate substantially in the horizontal plane, thereby causing the skate to experience enhanced turning. Conventional skateboards have turning mechanisms that operate in generally the same way.
Among other disadvantages of this arrangement, it is often not conducive to the use of wheels significantly larger than those normally used in the art. Larger wheels may be desirable because they travel more smoothly over bumpy, uneven, or textured surfaces such as dirt, cobblestones, and cracks and grooves in cement. Usually, wheels of any size are mounted on the underside of a platform such that the wheels are entirely below the level of the platform. Large wheels therefore require a higher platform, which may cause instability due to a high center of gravity. One way to avoid this problem is to configure the trucks such that the wheels are outside the perimeter of the platform, thus allowing for a lower platform than would be possible if the wheels were directly beneath the platform. However, this may cause the platform to interfere with the movement of the trucks and wheels. For example, since the wheels are mounted on the ends of the pivoting trucks, they have a wide range of movement and may come into contact with the platform while turning. This is especially likely when the wheels are large. Various modifications to the wheels, trucks, and/or platform can be devised to avoid this, but these tend to require sacrifices of simplicity and convenience. For example, mounting the wheels farther away from the platform reduces the chance of their hitting the platform, but also increases the size of the wheeled device, thus making it less portable.
The turnable wheel assembly disclosed in U.S. Pat. No. 7,306,240, by the same inventor, although designed with the preferred embodiment being an inline skate, may also be applied to a “quad” wheel arrangement. The distinguishing feature of the turnable wheel assembly in the '240 patent is that the orthogonal distance between the two parallel wheels, as well as the orthogonal distance between either of the wheels and the centerline of the skate, remains substantially the same during a turn. This enables the two wheels to be placed very close together without the risk of the wheels coming into physical contact while turning. This can be configured for the purposes of the present invention by spacing the wheels farther apart so that they are outside of the perimeter of the platform or base, thus achieving a similar result. However, the present invention is better suited to the purpose of the “quad” wheel arrangement because it is mechanically simpler.
A need thus exists for a wheeled device, having paired wheels larger than those normally used in the art, that provides enhanced turnability. Needs also exist for such a wheeled device that is relatively compact, lightweight, and mechanically simple.